Hot isostatic pressing (HIP) is a technology that finds more and more widespread use. Hot isostatic pressing is for instance used in achieving elimination of porosity in castings, such as for instance turbine blades, in order to substantially increase their service life and strength, in particular the fatigue strength. Another field of application is the manufacture of products, which are required to be fully dense and to have pore-free surfaces, by means of compressing powder.
Furthermore, yet another application is treatment of a load containing substances that, untreated, may emit volatile gases or dust in order to make them compact and dense and thereby eliminate or at least significant reduce their ability to make dust or emit substances. Thereby, the ability of the treated substances to endure storage and withstand impact from environmental factors such as oxygen and water is also significantly improved. This, in turn, improves the long-term stability of the treated substances and enables storage over long periods of time.
In certain applications, the substances are dangerous, e.g. radioactive materials or substances or poisonous or toxic material or substances, which entails that the handling of the substance has to be very careful in order to avoid, for example, any dust making. This applies during transport and storage of the substance, as well as during loading of the substances into the pressing arrangement, the actual treatment of the substance in the pressing arrangement and unloading of the substances. To this end, the substance is placed in sealed containers and the substance is kept within the containers during transport, treatment and storage.
In a hot isostatic pressing process, the containers are typically placed in a load compartment of an insulated pressure vessel. A cycle, or treatment cycle, comprises the steps of: loading, treatment and unloading of containers, and the overall duration of the cycle is herein referred to as the cycle time. The treatment may, in turn, be divided into several portions, or stages, such as a pressing stage, a heating stage, and a cooling stage.
After loading, the vessel is sealed off and a pressure medium is introduced into the pressure vessel and the load compartment thereof. The pressure and temperature of the pressure medium is then increased, such that the containers are subjected to an increased pressure and an increased temperature during a selected period of time. The temperature increase of the pressure medium, and thereby of the substance, is provided by means of a heating element or furnace arranged in a furnace chamber of the pressure vessel. The pressures, temperatures and treatment times are of course dependent on many factors, such as the material properties of the treated substance.
When the pressing treatment of the substance is finished, the containers including the substance often need to be cooled before being removed, or unloaded, from the pressure vessel.
In case of a container failure during the treatment of the substance in the pressing arrangement, there is an evident risk that substances leak from the damaged containers and contaminate the pressing arrangement, or in worst case, contaminate the surrounding environment. If the failure occurs at a high pressure, the effects may be very serious or even fatal. If the pressing arrangement is completely contaminated, the process of cleaning or decontaminating the pressing arrangement would be very expensive and parts of the pressing arrangement would have to be replaced and in worst case the pressing arrangement has to be destructed. If the substance leaks out from the pressing arrangement and into the surrounding environment, the effects on the environment may be very severe in case of a radioactive or poisonous substance.
Accordingly, it is of a very high importance that the effects of a potential container failure are kept at minimum and that the treated substance, in particular in case of a dangerous substance such as a radioactive substance, is isolated within the pressing arrangement in as small region as possible to avoid that the substance is spread in an uncontrolled manner in the pressing arrangement and in worst case further out in the surrounding environment.